Scientists have hailed the "unprecedented" results of a trial of a malaria vaccine that halved the incidence of severe disease in children over 18 months.
The success of the trial involving more than 1,400 children aged one to four in Mozambique has raised hopes that a vaccine can be created against malaria - a disease that kills more than one million people a year.
Researchers have been working on a malaria vaccine for more than 20 years, but, until now, none of the candidates has showed promise. The vaccine used in the latest trial is the most advanced among more than a dozen experimental vaccines being studied in humans.
The results were presented yesterday at an international malaria conference attended by 1,500 scientists, health workers and politicians in Cameroon.
Early trials of the vaccine reported last year showed it was effective over six months. The new study of the children who have been followed up for 18 months, published in the online edition of The Lancet, has shown that the efficacy of the vaccine did not wane and protection was maintained. The incidence of malaria among the children was reduced by more than a third and the risk of severe malaria, which kills thousands of children every week, was cut by 49 per cent.
Pedro Alonso, head of the Centre for International Health at the Hospital Clinic of the University of Barcelona, said in a statement: "The unprecedented response demonstrated in this study is further evidence that an effective vaccine to help control the malaria pandemic ... is very possible."
Researchers have accepted that, at least for the foreseeable future, there is no prospect of a vaccine that would wipe out malaria the same way that the smallpox vaccine did, or even provide lifelong immunity.
But a vaccine that would turn the disease into a mostly mild infection would make a huge dent in the effort to control malaria, which kills a child every 30 seconds and poses a threat to half of all people on the planet.
About 500 million episodes of malaria, which is caused by a parasite transmitted by mosquitoes, occur every year, mostly in the developing world. It is the leading killer of children under the age of five in sub-Saharan Africa.
Resistant parasites limit the effectiveness of existing medicines. A vaccine that trains the body's immune system to fight off infection by the malaria parasite may be the most effective way to control the disease, health experts say.
"Several more years of clinical investigation will be needed before this vaccine is ready for licensing and implementation but today's results move us an important step closer to developing a vaccine that can provide lasting protection to help save millions of lives," said Jean Stephenne, President of GSK Biologicals, which has been working on the development of the vaccine for 15 years. "The world should now take all required actions in order to get this vaccine to all the people who need it."
The Malaria Vaccine Initiative (MVI), one of several global health groups which are supported by the billionaire Microsoft founder Bill Gates, is financing the trials. In October, the Bill and Melinda Gates Foundation announced a $107m (£55m) grant to support the work. The vaccine may be on the market in 2011 if additional trials prove its effectiveness.
Melinda Moree, the director of MVI, said: "The ability of this vaccine to protect children from severe malaria for at least 18 months makes it a very promising potential public health tool for the developing world."
She added: "We are committed to making an affordable, safe, and effective malaria vaccine available as quickly as possible to those who need it most."